[GHC] #3169: Bad occurs-check error message

[GHC]

#3169: Bad occurs-check error message
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  Reporter:  simonpj                  |          Owner:                  
      Type:  bug                      |         Status:  closed          
  Priority:  low                      |      Milestone:  7.0.2           
 Component:  Compiler (Type checker)  |        Version:  6.10.2          
Resolution:  fixed                    |       Keywords:                  
  Testcase:  gadt/T3169               |      Blockedby:                  
Difficulty:  Unknown                  |             Os:  Unknown/Multiple
  Blocking:                           |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown             |  
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Changes (by simonpj):

  * status:  new => closed
  * testcase:  => gadt/T3169
  * resolution:  => fixed


Comment:

 Happily with the new type checker the error message is almost exactly as I
 said it should be 22 months ago:
 {{{
 T3169.hs:13:13:
     Couldn't match type `elt' with `Map b elt'
       `elt' is a rigid type variable bound by
             the type signature for
               lookup :: (a, b) -> Map (a, b) elt -> Maybe elt
             at T3169.hs:12:3
     Expected type: Maybe (Map b elt)
       Actual type: Maybe elt
     In the return type of a call of `lookup'
     In the expression: lookup a m :: Maybe (Map b elt)
 }}}
 I've added a regression test, and will close.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3169#comment:8>
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